In the conventional method and apparatus for manufacturing tapes or rolls of plastic film using, for example, a polymer film such as polypropylene, the polypropylene film is continuously extruded using a conventional process such as a tubular film or a T-die process. The resultant extruded or molded film is cut to a predetermined width by passing the film through a slitter to cut off excess material from each side edge of the film. In a later step, the film is cut into tapes having predetermined widths by slitting the film with the resultant tapes continuously collected onto take-up rollers. To avoid damage to the film, the take-up rollers are designed to avoid lengthwise creasing of the film and to minimize film weaving on a take-up core. This in turn avoids lateral displacement of successive tape layers causing irregular or uneven side edges of the rolled tape.
There are two general types of winders for collecting film tapes which include slitting equipment, known as center winders and surface winders. These winders are adapted to prevent weaving of the film tapes onto the take-up rollers by controlling the collection process such that air is not trapped between the product roll, i.e. collecting core, and the extruded film FIGS. 2(a) and 2(b) are schematic diagrams of typical center and surface winders, respectively.
In the center winder configuration of FIG. 2(a), polypropylene film 3 provides by main supply roller 6 is slit in half, each half constituting a polypropylene tape which is guided to a respective touch roller 1. Each touch roller 1 is in contact with a respective take-up roller 2 onto which polypropylene tapes 3 are wound. In the surface winder configuration of FIG. 2(b), polypropylene film 3 is slit in half as it passes to a single touch roller 7. Each tape 3 is guided onto respective take-up rollers 2 angularly displaced about touch roller 4. In both configurations, the touch roller(s) guide the polypropylene film 3 and minimize wrinking and creasing of the polypropylene film 3 as the film is wound onto the respective take-up rollers 2.
In either configuration, the touch rollers may have a soft flexible covering made of rubber or polyurethane material. However, rubber and polyurethane covered rollers are prone to pick up minute foreign materials, such as dust, which is attracted to the roller by static electricity accumulated on the roller. The foreign material can be adsorbed and embedded into the relatively soft rubber or polyurethane surface of the roller. This produces an irregular roller surface which deforms the film passing over the roller with each rotation. The resultant surface flaws made in the collected film tape degrades the electrical insulation characteristics of the film. Thus, rubber or polyurethane covered touch rollers are unsuitable for producing films used for electrical insulation such as dielectric material of capacitors.
Metallic rollers having a grooved surface are known alternatives to flexible rubber or polyurethane covered touch rollers. However, a grooved metallic roller of this type is apt to have sharp protrusions in its surface. These sharp protrusions may cause defects in the film including small pinhole punctures of the film produced as the film passes over the touch roller. To avoid such damage to the film, it was considered necessary that the contacting surfaces of such metallic touch rollers are made very smooth. For example, the surface of a metallic touch roller may be plated with a metal, such as chromium, which is polished to achieve a specular gloss finish. However, when a roller has such a smooth surface, the plastic polymer film tends to slip across and over the roller surface resulting in weaving of the collected film with resultant decreased production efficiency.